In inhalation therapy it is of utmost importance that the diameter of particles of the medicament to be inhaled is less than 10 .mu.m to ensure the adequate penetration of the particles into the bronchial region of the lungs.
When the medicament is composed of particles having diameters less than 10 .mu.m, the interparticular forces are generally greater than the force of gravity and consequently the material is cohesive. Non-defined agglomerates or aggregates form at random when this finely divided powdered medicament is handled, for instance during storage, conveying, sieving, sifting, mixing or grinding.
When using dry powder inhalers and especially breath-actuated dry powder inhalers it is therefore important that the inhalation device is provided with means which break down just before or during inhalation the said agglomerates or aggregates formed from the finely divided powder into the primary particles having a particles size within the respiratory range, of less than 10 .mu.m, preferably less than 5 .mu.m.
If the particle aggregates are bigger than 10 .mu.m they will not penetrate to the bronchial region of the lungs but will end up in the oro-laryngeal tract or, if swallowed, in the gastrointestinal tract where they could lead to unwanted side-effects. Particle aggregates could also more easily be retained in the device which also leads to a loss of particles which will have a negative effect on the exactness of the doses.
Means for breaking down agglomerates/aggregates of powder created in finely divided powdered medicaments having a primary of less than 10 .mu.m are known in the prior art. One example of such means is described in EP-B-069 715. In this document a rotating, propeller-like device is provided in the air conduit as deagglomeration means. Another example is described in EP-B-237 507, where a stationary deflector device is provided in the mouth-piece and/or the air conduit of a breath-actuated dry powder inhaler having a container for multiple doses. These stationary deflector devices will, during inhalation, provide a deaggregating effect as they are constructed to create a turbulent movement in the air flow carrying the substance. Due to this turbulent movement the particles will impact on the walls of the air conduit and the deflector devices and collide with each other and in this manner break down into primary within the respiratory range.
In WO 92/04069 a disposable breath-actuated dry powder inhaler for single use is disclosed. This inhaler is provided with means for breaking down agglomerates /aggregates in the air conduit. The deagglomerating means in this inhaler are also constructed to create a turbulent movement in the air flow during inhalation. This is achieved as all of the deagglomerating means are constructed as planar surfaces oriented about 30.degree. relative to the longitudinal direction of the tubular housing of the inhaler.
Tests have shown that the above mentioned deaggregation means do not give an optimum deaggregation effect. In some cases retention in the inhaler could reach an unacceptable level. This could lead to different dosages with different inhalations.